SIGNAL PROCESSING

BACKGROUND/HISTORY
The Environmental Sciences Laboratory has a long history of developing state of the art signal processing algorithms. These algorithms, developed since the mid-1980s, have been installed in many Naval SONAR systems. ESL’s signal processing sponsors include SPAWAR, NAVSEA, ONI, ONR, and DARPA. Brief descriptions of some of ESL’s signal processing efforts are below.

ALGORITHM DESCRIPTIONS
ESL is involved in several areas of signal processing. The staff within ESL are acknowledged leaders in the fields that include conventional and adaptive beamforming, broadband processing, matched field processing and active signal processing.

ADAPTIVE BEAMFORMING
ARL:UT is active in the development of new adaptive beamforming algorithms. Beamforming allows arrays of sensors to discriminate between signals in one direction and noise in other directions. ESL has used adaptive beamforming to improve SONAR performance in fixed and towed array sensors. ESL uses its understanding of environmental acoustics to design algorithms that take advantage of the noise enviroment within the ocean. These algorithms exploit the noise directionality and adapt, as the noise environment changes, to maximize the system performance, providing the operator with enhanced detection capability. This figure shows noise from an array, where an interferer is causing significant noise in all directions, when the array is beamformed using a conventional beamformer. The interferer is clear near the right side of the display, as the yellow and orange area that is cycling on and off. This interferer can be considered to be a jammer for the array, and the conventional beamformer sidelobes are not sufficiently low to restrict its azimuthal influence (i.e., the interferer is seen in all directions, albeit at lower levels when the beam is pointed away from the source). The noise from the adaptive beamformer, in contrast, shows enhanced noise characteristics in that the interferer at the right side of the noise field is significantly limited in its extent, the noise to the left is not affected by the jammer, and other contacts are visible (blue-green streaks on the left). Since the noise is much less with ABF, it will allow the SONAR operator to see targets of interest at much greater distances, enhancing detectability.

BROADBAND PROCESSING
ARL:UT and ESL are acknowledged experts in the area of developing broadband processing and display algorithms for Naval SONAR systems. ARL:UT developed the crosscorrelation processing scheme currently used several Navy systems. ESL continues to refine crosscorrelation and energy detection algorithms, providing superior situational awareness and detection capability to the SONAR operator.

MATCHED FIELD PROCESSING
Although adaptive beamforming can provide significant gains in performance, in some environments, and for some tactical situations, matched field processing can provide additional gains or information. Matched field processing couples signal processing with a thorough understanding of the acoustic environment. Environmental models are used to define signal representations used in the signal processing algorithms. This requires advanced simulation modeling capability. The signal representations are then used in specially designed signal processing algorithms to extract information on the contacts of interest.

SUMMARY
ARL:UT and ESL are known leaders in the SONAR signal processing arena. Advances in performance within a variety of systems, courtesy of ARL:UT technology, have improved the US Navy’s capabilities all over the world. ESL’s work in signal processing continues to hold promise for further enhancements, and exciting opportunities to influence and improve SONAR systems will continue to exist for many years to come.

For more information, E-mail: esl_director@arlut.utexas.edu

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